But now a new wave of ailments may be striking the 240,000 men and women who worked on the front lines of the disaster. Cataracts, a hallmark affliction of atom-bomb survivors in Japan, are on the rise. More worrisome, a study of Russian liquidators blamed the accident for 230 "excess" deaths in the 1990s—from heart disease as well as leukemia and other cancers.

The connection between Chernobyl and heart disease is controversial. Blasts of radiation can damage blood vessels, but some scientists believe the elevated rate of heart disease among the liquidators is more likely the result of heavy drinking and smoking, stress, and a poor diet. The cancer spike among the liquidators, however, was long expected, and the smattering of cases so far could be just the beginning. Jacov Kenigsberg, the chairman of the National Commission of Radiation Protection of Belarus, notes that it took 20 to 25 years for some radiation-induced cancers to appear in the atom-bomb survivors. "We can say that we're on the beginning of the road."

The millions of ordinary people who had the bad luck to live downwind of Chernobyl are also at risk. The initial explosion rained radioactive material to the west of the reactor, sparing Pri-pyat a direct hit while killing a swath of pines that became known as the Red Forest for the eerie red needles of the dead trees. "The winds were very, very fortunate," says Ronald Chesser, an ecologist at Texas Tech University who is studying the plume as a model of what might happen if a radioactive dirty bomb exploded in an American city.

Then, as the reactor burned out of control, winds swept the cloud north. Seventy percent of the radioactivity drifted into Belarus, contaminating nearly a quarter of the country. Yet the Soviet government left people there in the dark. While children in Pripyat were taking iodine pills hours after the explosion, authorities in Belarus did not begin distributing pills for a week or more. All that time children were drinking milk laced with radioactive iodine 131 from cows that had grazed on contaminated grass. The short-lived, powerful isotope made its way to the thyroid gland, which has an afﬁnity for iodine.

Starting in 1990, Alexei Okeanov and others observed the consequences: a sharp rise in childhood thyroid cancer. "It was absolutely obvious it was due to Chernobyl, but it was very hard to prove," Okeanov says. Before Chernobyl, Belarus had two or three cases a year in children under the age of 15. In 1995 there were 90 cases. To date about 4,000 children and teenagers in Belarus, Russia, and Ukraine have been diagnosed with the cancer, the largest fraction of them from Homyel, a heavily contaminated region of Belarus just north of Chernobyl. Although thyroid cancer has one of the highest cure rates of any malignancy, at least nine children died when their tumors spread, and survivors must spend a lifetime on medication.